“…California patients were genotyped; all were measles genotype B3, which has caused a large outbreak recently in the Philippines…”

Measles Outbreak — California, Dec 2014–Feb 2015

It wasn’t a vaccine strain.

Outbreaks

Year

Genotype

Minnesota

2017

B3

Tennessee

2016

B3

California

2015

B3

Florida

2013

D8

California

2014

B3, D8

Brooklyn

2013

D8

North Carolina

2013

D8

Minnesota

2011

B3

Washington, Illinois

2008

D5, D4

For example, during 2011, 222 cases of measles and 17 outbreaks were reported in the United States, with most cases originating from just five countries (France, Italy, Romania, Spain, and Germany). Six different genotypes were identified, including B3, D4, G3, D8, H1, and D9. No vaccine strains…

And no, it doesn’t matter that the vaccine strain of measles, genotype A, differs from all of the wild strains of measles we see in the outbreaks.

“Vaccine induced immunity protects against all virus strains. Measles is considered a monotypic virus despite the genetic variations.”

Factsheet about measles

Unlike the flu, HPV, and pneumococcal bacteria, in which vaccines only protect against different serotypes, in the case of measles, the genotype simply helps us figure out where the measles case came from.

But if it isn’t the vaccine strain, then why do they that is it important to rapidly identify wild strains vs vaccine strains?

“During measles outbreaks, it is important to be able to rapidly distinguish between measles cases and vaccine reactions to avoid unnecessary outbreak response measures such as case isolation and contact investigations.”

Outbreaks typically trigger a lot of folks to get vaccinated. While that’s great, one possible problem is that some of those folks might develop a fever and/or rash after their MMR vaccine. So it is important to quickly figure out whether they are part of the outbreak and have a wild strain (maybe they were exposed before their vaccine could start to work) or are having a common, mild vaccine reaction.

But couldn’t they have vaccine-associated measles if they have a rash and fever and a vaccine strain? Theoretically, but then they would likely have true measles symptoms. And even in these rare case reports, the children didn’t spread the measles to anyone else.

So why are you waiting to know the genotype of the measles strain causing the outbreak in your area? Hopefully, it isn’t to help you decide whether or not to vaccinate and protect your kids. While it is interesting to know where the outbreak originated, you can bet that it isn’t a vaccine strain.